This invention relates generally to photographic apparatus employing means for artificially illuminating a scene to be photographed and, more particularly, to photographic apparatus employing means for automatically selecting operative flash lamps, from an array comprising both operative and inoperative flash lamps, for effecting a photographic exposure.
Photographic flash systems in which a plurality of flash lamps are assembled within a disposable mounting have been favorably received by the consuming public. Certain of these mountings are fashioned as a cubic package in which four flash lamps and associated reflectors face outwardly through four surfaces of the cubic form and have come to be known as "flashcubes". The surfaces are moved sequentially into a flash illuminating orientation by a mechanical rotation assembly coupled with an exposure mechanism of a camera. Sequential switching between the flash lamps within the cube is accomplished as an adjunct to the mechanical rotation of the lamp mounting. Should an inoperative flash lamp be encountered in the course of taking flash illuminated photographs with the cube, the attempted exposure will be aborted, usually with an attendant loss of a frame of film.
In another multiple flash lamp arrangement, a plurality of flash lamps are mounted as an array within a singular disposable package. Typically, these units include a base member which supports a coplanar array of flash lamps and individual lammp reflectors behind each lamp. The lamps may be arranged in a single row, i.e., a linear array, or in other embodiments may be disposed in two or more interdigitated or parallel rows. The base member is adapted to be connected to a socket on the camera which aligns all of the lamps on the array in a direction such that their light output is substantially parallel with the optical axis of the camera's objective lens. The base member generally includes an insulating terminal board which supports a plurality of thin film conductive paths that are connected at one end to the lamp filament wires. Generally, there is one common conductive path to which one end of all of the lamp filaments are connected. The opposite end of the lamp filaments are each connected to their own individual conductive path. Accordingly, contact to any lamp in the array may be made by making contact simultaneously to the common path and the individual paths.
Linearly arranged multiple flash lamp arrays such as described above have come to be known as "Flash-Bars" and in operation all of the lamps are oriented for providing scene illumination when ignited without recourse to moving or rotating either the flash lamps or their mountings between exposures. Examples of the type of multi-lamp flash units broadly described above may be found in U.S. Pat. Nos. 3,598,984 issued to Slomski and U.S. Pat. No. 3,598,985 issued to Harnden et al. on Aug. 10, 1971. Since no relative movement of the flash lamps is involved between exposures, switching systems are required to cause synchronous igniting of individual bulbs with each actuation of a photographic exposure system. Generally, firing circuits are provided which sequentially ignite the bulbs in a predetermined order from first to last with each actuation of a flash shutter synchronization switch. For example, U.S. Pat. No. 3,608,451, issued to Kelem on Sept. 28, 1971, discloses the use of a multi-contact switch having a rotary contact wiping member. The common lamp terminal is connected to one electrode of a battery within the camera. The individual lamp terminals are each connected to a separate contact on the switch. The contact wiping member is connected to the other battery electrode through a normally open flash ignition switch. After one lamp has been ignited, the flash lamp ignition switch is reopened and the contact wiping member is rotated one station to connect the next lamp in the array to the flash firing circuit.
In another arrangement, Goshima et al. in U.S. Pat. No. 3,438,315, issued on Apr. 15, 1969, discloses a multi-flash arrangement for cameras in which a plurality of flashbulbs can be either automatically or manually connected to a firing circuit. The firing circuit includes a battery and capacitor, a flash synchronizing contact, and a mechanical switch arm. The switch arm connects each of the flashbulbs sequentially to the firing circuit and is adapted for automatically switching as the film advances or for manual selection of the flashbulbs by a selector switch on the face of the camera.
A variety of other sequencing circuits for firing flashbulbs in successional order have been proposed. In one category of these circuits, sensing elements are arranged to respond to the heat or light output of an igniting flashbulb by varying either a mechanical or electrical parameter. Following this parameter variation, the circuits enable or arm select lamps within an array for successive firing. In most cases, however, such sequencing devices are either self-destructing when used or require excessive packaging volumes for camera mounted applications. Additionally, the systems are incapable of bypassing any inoperative flashbulbs which may be present in an array.
In still another arrangement, a cascading assembly of electrical resistors or the like is selectively coupled within a grouping of flash lamp circuits. During operation, lamp igniting currents are selectively attenuated to cause the flash lamps within the circuits to be fired in succession. In addition to being somewhat insensitive to any variations in power supply or circuit performance, this form of successive system is also incapable of bypassing inoperative flash lamps within an array and must rely on an open circuit condition at the terminals of any expended lamp to continue a lamp sequencing function.
In U.S. Pat. No. 3,618,492, issued to Ellin on Nov. 9, 1971, a photographic flash exposure system is described which is operative to sequentially ignite individual lamps within an array of flash lamps. The system automatically passes a monitoring current through each of the flash lamps during each exposure cycle to derive alignment signals which function to align a flash lamp sequencing circuit to bypass inoperative flash lamps. The Ellin device, while workable, provides a system of complex electronic networks and it is both difficult of manufacture and expensive.
In my copending applications Ser. Nos. 427,812 and 427,938 filed on even date and commonly assigned herewith, there are described electromechanical systems for automatically selecting operative flash lamps from an array of operative and inoperative lamps. These systems, while simple and effective, require either that a switch be mechanically intercepted each time a flash lamp is ignited or that the motion of the switch and the charging time of a capacitor be very precisely controlled.